What is molecular formula for polyester?

Polyester is a polymer consisting of ester units. When a dihydric alocohol like Ethylene

glycol reacts with a aromatic acid like Phthalic acid with two acid groups, the reaction can proceed under suitable conditions to make a polymeric ester " Polyester"

One OH group of one alcohol molecule reacts with one COOH Croup of the phthalic acid, and the remaining COOH group of the acid reacts with another OH group of another alocohl and thus reacts alternativerly alcohol and acid to form a chain of polymeric Polyester.

2 (HO.CH2.CH2.OH) + HOOC.C6H4.COOH -> HO.CH2.CH2.COO.C6H4.COO.CH2.CH2.OH + 2 H2O

iTREACTS FURTHER WITH MORE PHTHALIC ACID TO GIVE

HO. n(CH2.CH2.COO.C6H4.COO.) CH2.CH2.OH